This invention relates to an improved catalytic composite and process for the conversion of hydrocarbons, and more specifically for the selective upgrading of a paraffinic feedstock by isomerization.
The widespread removal of lead antiknock additive from gasoline and the rising fuel-quality demands of high-performance internal-combustion engines have compelled petroleum refiners to install new and modified processes for increased xe2x80x9coctane,xe2x80x9d or knock resistance, in the gasoline pool. Refiners have relied on a variety of options to upgrade the gasoline pool, including higher-severity catalytic reforming, higher FCC (fluid catalytic cracking) gasoline octane, isomerization of light naphtha and the use of oxygenated compounds. Such key options as increased reforming severity and higher FCC gasoline octane result in a higher aromatics content of the gasoline pool at the expense of low-octane heavy paraffins.
Refiners are also faced with supplying reformulated gasoline to meet tightened automotive emission standards. Reformulated gasoline differs from the traditional product in having a lower vapor pressure, lower final boiling point, increased content of oxygenates, and lower content of olefins, benzene and aromatics. Benzene content generally is being restricted to 1% or lower, and is limited to 0.8% in U.S. reformulated gasoline. Gasoline aromatics content is likely to be lowered, particularly as distillation end points (usually characterized as the 90% distillation temperature) are lowered, since the high-boiling portion of the gasoline which thereby would be eliminated usually is an aromatics concentrate. Since aromatics have been the principal source of increased gasoline octanes during the recent lead-reduction program, severe restriction of the benzene/aromatics content and high-boiling portion will present refiners with processing problems. These problems have been addressed through such technology as isomerization of light naphtha to increase its octane number, isomerization of butanes as alkylation feedstock, and generation of additional light olefins as feedstock for alkylation and production of oxygenates using FCC and dehydrogenation. This issue often has been addressed by raising the cut point between light and heavy naphtha, increasing the relative quantity of naphtha to an isomerization unit. The performance of light-naphtha isomerization catalysts thus is increasingly important in refinery economics.
U.S. Pat. No. 2,939,896 B1 teaches isomerization of paraffinic hydrocarbons using a catalyst containing platinum, halogen and a sulfate of aluminum, magnesium and/or zirconium deposited on activated alumina. The patent does not disclose additional metal components of the catalyst, however. U.S. Pat. No. 5,036,035 B1 teaches a catalyst, and its use in isomerization, containing sulfated zirconium oxide or hydroxide and a platinum-group metal. The patent teaches that reduction of the platinum-group metal is not favorable.
U.S. Pat. No. 4,918,041 B1, U.S. Pat. No. 4,956,519 B1 and European Patent Application 0 666 109 A1 disclose a sulfated catalyst, and its use in isomerization, comprising an oxide or hydroxide of Group III or Group IV; oxide or hydroxide of Groups V, VI or VII; and oxide or hydroxide of Group VIII; ""109 also discloses a component from a list of Group VIII metals and metal combinations.
U.S. Pat. No. 3,915,845 B1 discloses a catalyst and its use comprising a platinum-group metal, Group IVA metal, halogen and lanthanide in an atomic ratio to platinum-group metal of 0.1 to 1.25. U.S. Pat. No. 5,493,067 B1 teaches that isoparaffins and olefins are alkylated by contact with a solid superacid such as sulfated zirconia optionally containing added metals and containing added heteropolyacids or polyoxoanions.
U.S. Pat. No. 5,310,868 B1 and U.S. Pat. No. 5,214,017 B1 teach catalyst compositions containing sulfated and calcined mixtures of (1) a support containing an oxide or hydroxide of a Group IV-A element, (2) an oxide or hydroxide of a Group VI, VII, or VIII metal, (3) an oxide or hydroxide of a Group I-B, II-B, III-A, III-B, IV-A, V-A metal, and (4) a metal of the lanthanide series.
U.S. Pat. No. 5,212,136 B1 discloses a solid super acid catalyst useful in alkylation processes comprising sulfated and calcined mixtures of a support of an oxide or hydroxide of a Group IV-A element, an oxide or hydroxide of molybdenum, and an oxide or hydroxide of a Group I-B, II-B, III-A, III-B, IV-B, V-A or VI-A metal other than molybdenum or a metal of the lanthanide series.
A purpose of the present invention is to provide an improved catalyst and process for hydrocarbon conversion reactions. Another purpose of the present invention is to provide improved technology to upgrade naphtha to gasoline. A more specific purpose is to provide an improved catalyst and process for the isomerization of light naphtha to obtain a high-octane gasoline component. This invention is based on the discovery that a catalyst containing ytterbium and platinum components provides superior performance and stability in the isomerization of light naphtha to increase its isoparaffin content.
A broad embodiment of the present invention is directed to a catalyst comprising a sulfated support of an oxide or hydroxide of a Group IVB (IUPAC 4) metal, preferably zirconium oxide or hydroxide, at least a first component which is a lanthanide element or yttrium component, and at least a second component being a platinum-group metal component. The first component preferably consists of a single lanthanide-series element or yttrium and the second component preferably consists of a single platinum-group metal. Preferably, the first component is ytterbium and the second component is platinum. The catalyst optionally contains an inorganic-oxide binder, especially alumina.
An additional embodiment of the invention is a method of preparing the catalyst of the invention by sulfating the Group IVB metal oxide or hydroxide, incorporating a first component, a lanthanide element, yttrium, or any mixture thereof, and the second component, a platinum-group metal, and preferably binding the catalyst with a refractory inorganic oxide.
In another aspect, the invention comprises converting hydrocarbons using the catalyst of the invention. In yet another embodiment, the invention comprises the isomerization of isomerizable hydrocarbons using the catalyst of the invention. The hydrocarbons preferably comprise light naphtha which is isomerized to increase its isoparaffin content and octane number as a gasoline blending stock.
These as well as other embodiments will become apparent from the detailed description of the invention.